INVESTIGATIONS ON THE VISCOSITY DEPENDENCE OF PHOTOINDUCED ELECTRON-TRANSFER PROCESSES IN LIQUID SOLUTIONS

In order to investigate the viscosity dependence of the reaction of ph otoinduced perylene with tetracyanobenzene and N,N-2,4,6-pentamethylan iline in acetonitrile fluorescence quenching measurements have been pe rformed, respectively. To increase the viscosity several highly viscou s substances (ethyleneglycole, polyethyleneglycole, tetramethylurea) h ave been added. In the first two cases the dependence of the quenching rate constant, kQ, on viscosity does not follow the Einstein-Smolucho wski equation. It is concluded that it is not possible to investigate viscosity dependences of electron transfer reactions in these two solv ent mixtures because the reactions proceed in an acetonitrile-like env ironment. Better results are obtained for the reaction of perylene wit h the amine using an acetonitrile/tetramethylurea mixture.